Hose-type packing wrappers shirred to form caterpillars of the type as described hereinbefore are being widely used, especially in sausage fabrication, on automatic filling machines. By previously closing a wrapper end, it is possible, after mounting the packing wrapper onto the loading tube, to immediately commence the filling operation. However, it is desirable to vent the packing wrapper at the closed end to prevent air pads from being formed. An end closure of a twisted plait-type configuration containing a venting channel is suitably used for that purpose.
According to a state-of-the-art method for forming an end closure of this type (DE-OS 23 17 867), a plurality of key-shaped plates are provided in radial planes on the front-sided end of a rotatingly drivable cylindrical tool carrier. Front edges of the tool carrier are disposed on a conical surface and the shaped plates are forced against the front-sided end of the shirred packing wrapper, thereby exerting a circumferential force on the hose type wrapper material as used therein. This progressively draws out the ultimate folds of the shirred packing wrapper within the latter, twisting them about an elongated thin shaping element projecting into the packing wrapper to form a closely twisted knot of hose-type wrapper material about the shaping element. However, it is not indicated how to proceed to reach this goal by the means shown and described.
In another conventional method according to DE-PS 34 05 445, the front-sided end of a caterpillar is twisted in relation to the remainder by means of a pair of tongs, thereby providing a tight closure with no vent orifice.
According to another conventional method for forming an end closure in the form of a twisted plaint within a packing wrapper shirred in caterpillar-type manner (U.S. Pat. No. 4,536,175), a rotatingly actuable shaft carries two axially parallel gripper claws of different length between which is manually introduced the end of the packing wrapper after drawing out the ultimate folds. The gripper is then pushed into the packing wrapper. After that, a non-rotating buffer with the conical front side thereof is placed against the end of the packing wrapper, with the gripper claws being rotated to form a twisted plait. The description and illustration of the method and the device for carrying out the method do not teach how the desired venting channel is formed in the twisted plait.
Finally, a method of providing an end closure in the form of a twisted plait containing a vent channel on a packing wrapper shirred in caterpillar-type manner is taught by DE-OS 31 41 782. This method is being widely used in the art, as opposed to the afore-described method. According to this method an elongated shaping element from the rear side is guided throughout the packing wrapper, and the ultimate folds of the packing wrapper are twisted about the shaping element through externally seizing and rotatingly actuated clamping jaws. The twisting plait thereby formed externally of the packing wrapper is then forced into the packing wrapper through a sleeve-type element. Although a faultless end closure containing the desired vent channel is attained in this manner, the method as used, in view of the additional measure of forcing the twisted plait into the shirred packing wrapper, is complex and time-consuming. In addition, execution thereof involves substantial space requirements and considerable mechanical efforts.